Kissing was developed 'to spread germs'

It isn't the most romantic theory, but scientists believe kissing was
developed to spread germs which build up immunity to illness.

Kissing helps to protect womenPhoto: GETTY IMAGES

8:00AM GMT 31 Oct 2009

They say the gesture allows a bug named Cytomegalovirus, which is dangerous in pregnancy, to be passed from man to woman to give her time to build up protection against it.

The bug is found in saliva and normally causes no problems. But it can be extremely dangerous if caught while pregnant and can kill unborn babies or cause birth defects.

Writing in the journal Medical Hypotheses, researcher Dr Colin Hendrie from the University of Leeds, said: "Female inoculation with a specific male's cytomegalovirus is most efficiently achieved through mouth-to-mouth contact and saliva exchange, particularly where the flow of saliva is from the male to the typically shorter female."

Kissing the same person for about six months provides the best protection, he added.

As the relationships progresses and the kisses become more passionate, the woman's immunity builds up, cutting her odds of becoming ill.